Integrated resuscitation

ABSTRACT

A resuscitation system for use by a rescuer for resuscitating a patient, comprising at least two high-voltage defibrillation electrodes, a first electrical unit comprising circuitry for providing resuscitation prompts to the rescuer, a second electrical unit separate from the first unit and comprising circuitry for providing defibrillation pulses to the electrodes, and circuitry for providing at least one electrical connection between the first and second units. In another aspect, at least two electrical therapy electrodes adapted to be worn by the patient for extended periods of time, circuitry for monitoring the ECG of the patient, an activity sensor adapted to be worn by the patient and capable of providing an output from which the patient&#39;s current activity can be estimated, and at least one processor configured for estimating the patient&#39;s current activity by analyzing the output of the activity sensor, analyzing the ECG of the patient, and determining whether electrical therapy should be delivered to the electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.application Ser. No. 11/928,087, filed Oct. 30, 2007, which is adivisional of Ser. No. 10/954,633, filed Sep. 30, 2004, now abandoned.The disclosures of each of the foregoing are hereby incorporated byreference in their entirety for all purposes.

This application is also a continuation of and claims priority to U.S.application Ser. No. 15/343,564, filed Nov. 4, 2016, which is acontinuation of and claims priority to U.S. application Ser. No.11/928,087, filed Oct. 30, 2007, which is a divisional of and claimspriority to U.S. application Ser. No. 10/954,633, filed Sep. 30, 2004,now abandoned. U.S. application Ser. No. 15/343,564, filed Nov. 4, 2016,is also a continuation application of and claims priority to U.S.application Ser. No. 12/794,719, filed Jun. 4, 2010, which is acontinuation of and claims priority to U.S. application Ser. No.10/954,633, filed Sep. 30, 2004, now abandoned. The disclosures of eachof the foregoing are hereby incorporated by reference in their entiretyfor all purposes.

This application is also a continuation of and claims priority to U.S.application Ser. No. 14/177,520, filed Feb. 11, 2014, which is acontinuation of and claims priority to U.S. application Ser. No.11/928,087, filed Oct. 30, 2007, which is a divisional of and claimspriority to U.S. application Ser. No. 10/954,633, filed Sep. 30, 2004,now abandoned. The disclosures of each of the foregoing are herebyincorporated by reference in their entirety for all purposes.

This application is also a continuation of and claims priority to U.S.application Ser. No. 13/271,613, filed Oct. 12, 2011, which is acontinuation of and claims priority to U.S. application Ser. No.12/794,719, filed Jun. 4, 2010, which is a continuation of and claimspriority to U.S. application Ser. No. 10/954,633, filed Sep. 30, 2004,now abandoned. The disclosures of each of the foregoing are herebyincorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

This invention relates to resuscitation systems incorporatingdefibrillation therapy and resuscitation prompts.

BACKGROUND OF THE INVENTION

Resuscitation can generally include clearing a patient's airway,assisting the patient's breathing, chest compressions, anddefibrillation.

The American Heart Association's Basic Life Support for Health CareProviders textbook provides a flow chart at page 4-14 of Chapter 4 thatlists the steps of airway clearing, breathing, and circulation (known asA, B, and C), for situations in which there is no defibrillator readilyaccessible to the rescuer.

Defibrillation (sometimes known as step D) can be performed with the useof an automatic external defibrillator (AED) Most automatic externaldefibrillators are actually semi-automatic external defibrillators(SAED), which require a clinician to press a start button, after whichthe defibrillator analyzes the patient's condition and provides a shockto the patient if the electrical rhythm is shockable and waits for userintervention before any subsequent shock. Fully automatic externaldefibrillators, on the other hand, do not wait for user interventionbefore applying subsequent shocks. As used below, automatic externaldefibrillators (AED) include semi-automatic external defibrillators(SAED).

Both types of defibrillators typically provide an oral stand clearwarning before the application of each shock, and then the clinician isexpected to stand clear of the patient and may be required to press abutton indicating that the clinician is standing clear of the patient.The controls for automatic external defibrillators are typically locatedon a resuscitation control box.

AEDs are used typically by trained providers such as physicians, nurses,fire department personnel, and police officers. There might be one ortwo people at a given facility that has an AED who have been designatedfor defibrillation resuscitation before an ambulance service arrives.The availability of on-site AEDs along with rescuers trained to operatethem is important because if the patient experiences a delay of morethan 4 minutes before receiving a defibrillation shock the patient'schance of survival can drop dramatically. Many large cities and ruralareas have low survival rates for defibrillation because the ambulanceresponse time is slow, although many suburbs have higher survival ratesbecause of the faster ambulance response time due to lack of traffic andavailability of hospitals and advanced life support.

Trained lay providers are a new group of AED operators, but they rarelyhave opportunities to defibrillate. For example, spouses of heart attackvictims may become lay providers, but these lay providers can be easilyintimidated by an AED during a medical emergency. Consequently, such layproviders can be reluctant to purchase AEDs, or might tend to wait foran ambulance to arrive rather than use an available AED, out of concernthat the lay provider might do something wrong.

There are many different kinds of heart rhythms, some of which areconsidered shockable and some of them are not. For example, a normalrhythm is considered non-shockable, and there are also many abnormalnon-shockable rhythms. There are also some abnormal non-viablenon-shockable, which means that the patient cannot remain alive with therhythm, but yet applying shocks will not help convert the rhythm.

As an example of a non-shockable rhythm, if a patient experiencesasystole, the heart will not be beating and application of shocks willbe ineffective. Pacing is recommended for asystole, and there are otherthings that an advanced life support team can do to assist such patient,such as the use of drugs. The job of the first responder is simply tokeep the patient alive, through the use of CPR and possiblydefibrillation, until an advanced life support team arrives.Bradycardias, during which the heart beats too slowly, are non-shockableand also possibly non-viable. If the patient is unconscious duringbradycardia, it can be helpful to perform chest compressions untilpacing becomes available. Electro-mechanical dissociation (EMD), inwhich there is electrical activity in the heart but it is not making theheart muscle contract, is non-shockable and non-viable, and wouldrequire CPR as a first response. Idio-ventricular rhythms, in which thenormal electrical activity occurs in the ventricles but not the atria,can also be non-shockable and non-viable (usually, abnormal electricalpatterns begin in the atria). Idio-ventricular rhythms typically resultin slow heart rhythms of 30 or 40 beats per minute, often causing thepatient to lose consciousness. The slow heart rhythm occurs because theventricles ordinarily respond to the activity of the atria, but when theatria stop their electrical activity, a slower, backup rhythm occurs inthe ventricles.

The primary examples of shockable rhythms, for which a first respondershould perform defibrillation, include ventricular fibrillation,ventricular tachycardia, and ventricular flutter.

After using a defibrillator to apply one or more shocks to a patient whohas a shockable electrical rhythm, the patient may nevertheless remainunconscious, in a shockable or non-shockable rhythm. The rescuer maythen resort to chest compressions. As long as the patient remainsunconscious, the rescuer can alternate between use of the defibrillator(for analyzing the electrical rhythm and possibly applying a shock) andperforming cardio-pulmonary resuscitation (CPR).

CPR generally involves a repeating pattern of five or fifteen chestcompressions followed by a pause. CPR is generally ineffective againstabnormal rhythms, but it does keep some level of blood flow going to thepatient's vital organs until an advanced life support team arrives. Itis difficult to perform CPR over an extended period of time. Certainstudies have shown that over a course of minutes, rescuers tend toperform chest compressions with less-than-sufficient strength to causean adequate supply of blood to flow to the brain. CPR prompting devicescan assist a rescuer by prompting each chest compression and breath.

PCT Patent Publication No. WO 99/24114, filed by Heartstream, Inc.,discloses an external defibrillator having PCR and ACLS (advancedcardiac life support) prompts.

SUMMARY OF THE INVENTION

In a first aspect, the invention features a resuscitation system for useby a rescuer for resuscitating a patient, comprising at least twohigh-voltage defibrillation electrodes, a first electrical unitcomprising circuitry for providing resuscitation prompts to the rescuer,a second electrical unit separate from the first unit and comprisingcircuitry for providing defibrillation pulses to the electrodes, andcircuitry for providing at least one electrical connection between thefirst and second units.

Preferred implementations of this aspect of the invention mayincorporate one or more of the following. The two electrodes and thefirst unit may be built into a defibrillation electrode pad assembly.The defibrillation electrodes may be detachable from the defibrillationelectrode pad assembly. The first unit may be separate from the twoelectrodes, and may be connected to the two electrodes by one or morecables. The first unit may be capable of functioning and providing theresuscitation prompts without being electrically connected to the secondunit. The first unit may comprise a source of electrical power and aprocessor. The first unit may have circuitry for monitoring at least onephysiological parameter of the patient. The parameter may be an ECGsignal. The resuscitation prompts may comprise CPR prompts. Thecircuitry for providing at least one electrical connection between thefirst and second units may comprise at least one cable. The circuitryfor providing at least one electrical connection between the first andsecond units may comprise at least one wireless connection. The secondunit may be connected directly to the defibrillation electrodes by oneor more cables that carry the defibrillation pulses to the electrodes.The circuitry for providing at least one electrical connection betweenthe first and second units may comprise at least one cable fordelivering the defibrillation pulses to the first unit, from where theyare delivered to the electrodes. The ECG signal may be detected usingthe defibrillation electrodes. The first unit may comprise a speaker forproviding the resuscitation prompts. The resuscitation prompts maycomprise spoken and visual prompts. The first unit may comprise amicrophone and circuitry for storing sounds recorded during use of theunit. The defibrillation electrodes may be built into an electrode padassembly and a handle for providing an upward lifting force on theassembly may be provided. The handle may comprise a flexible sheetmaterial. The handle may comprise a substantially rigid material.

In a second aspect, the invention features a resuscitation system forresuscitating a patient, comprising at least two electrical therapyelectrodes adapted to be worn by the patient for extended periods oftime, circuitry for monitoring the ECG of the patient, an activitysensor adapted to be worn by the patient and capable of providing anoutput from which the patient's current activity can be estimated, andat least one processor configured for estimating the patient's currentactivity by analyzing the output of the activity sensor, analyzing theECG of the patient, and determining whether electrical therapy should bedelivered to the electrodes.

Preferred implementations of this aspect of the invention mayincorporate one or more of the following. The processor may beconfigured for estimating whether the patient is moving. The activitysensor may comprise an accelerometer, and the processor may beconfigured for integrating the output of the accelerometer to provide anestimate of velocity and/or displacement. The processor may beconfigured to process the output of the activity sensor and use theresult of the processing to modify at least one threshold in a techniqueused for determining a physiological status of patient. Thephysiological status may comprise determining a risk of impending heartattack or cardiac arrest. The resuscitation system may include a speakerfor issuing spoken prompts to the patient, and the processor may decideon the nature of the spoken prompt based on the estimated currentactivity of the patient. The patient's current activity may compriseestimating the orientation of the patient. Estimating the orientation ofthe patient may comprise determining whether the patient lying on hisback. The electrodes may be defibrillation electrodes and the electricaltherapy may comprise a defibrillation pulse. The invention may furthercomprise an activity sensor adapted to be worn by the patient andcapable of providing an output from which the patient's current activitycan be estimated, and at least one processor configured for estimatingthe patient's current activity by analyzing the output of the activitysensor. The at least one processor may be located in the first unit. Atleast some of the resuscitation prompts delivered by the first unit maybe dependent on the estimated current activity of the patient. Thecurrent activity may comprise whether the patient is lying on his back,and at least one resuscitation prompt issued when the patient is not onhis back may be an instruction to roll the patient on their back priorto beginning CPR.

In a third aspect, the invention features a resuscitation system forresuscitating a patient, comprising at least two electrical therapyelectrodes adapted to be worn by the patient for extended periods oftime, circuitry for monitoring the ECG of the patient, an activitysensor adapted to be worn by the patient and capable of providing anoutput from which the patient's current activity can be estimated, andat least one processor configured for estimating the patient's currentactivity by analyzing the output of the activity sensor, analyzing theECG of the patient, and determining whether the patient has an elevatedprobability of cardiac arrest.

Preferred implementations of this aspect of the invention mayincorporate one or more of the following. The processor may beconfigured for determining whether the patient's current activityincludes increased physical activity. The processor may be configuredfor determining an activity level parameter representative of thepatient's activity level. The decision of an elevated probability ofcardiac arrest may be based on the activity level parameter and aparameter may be derived from the patient's ECG. The decision of anelevated probability of cardiac arrest may be based on the activitylevel parameter and a measurement of blood pressure. The invention mayfurther comprise the capability of delivering at least one test pulsethrough the electrodes at a time based, at least in part, on an estimateof the patient's current activity, wherein the test pulse is of a typeconfigured to produce a ventricular premature beat (VPB). The time basedon an estimate of the patient's current activity may be shortly afterwaking in the morning. Prior to delivering the test pulse, the systemmay issue a prompt to the patient requesting administration of the testpulse and the system may wait for the patient to indicate his consent toadministration of the test pulse.

Among the many advantages of the invention (some of which may beachieved only in some of its various aspects and implementations) arethat the invention may permit wider distribution and availability of thefirst unit, which provides resuscitation prompting, than of the secondunit, which provides defibrillation therapy. The first unit's relativelylower cost may make it possible for the first unit to be more widelydistributed than the second unit. Wider distribution of the first unitmay mean more successful rescues, as a patient can be stabilized andprepared for defibrillation using the first unit.

The unit may be worn on a continuous basis by a person at higher risk ofa heart attack such as someone who has recently undergone bypass surgeryor one who has experienced a myocardial infarction. The early warning ofa heightened risk of an impending cardiac arrest provided by the devicewill allow the wearer of the device to phone a physician or emergencyservice in advance of the actual cardiac arrest, thus reducing fatalityrates of cardiac arrest by early prevention and treatment of theunderlying physiological abnormalities rather than treating theconsequences of the arrest. The activity sensor provides a means ofdetermining whether or not the wearer of the device is awake or not,thereby providing an accurate way of providing voice prompts andphysiological tests in synchrony with the wearer's daily schedule in anon-interfering manner. When used in conjunction with a communicationlink to medical providers such as an EMS system, the activity sensoralso provides a means of determining the state of the victim, whetherthe victim is vertical or horizontal, and moving, thus potentiallylowering false alarm rates and accuracy of diagnosis. The activitysensor may also be used to adjust the thresholds used for various alarmsand heart attack risk detection methods. The wearer can activate akeying input on the device indicating chest pain, and in conjunctionwith the additional ECG, and activity sensor data, the device can morereliably calculate relative risk of impending heart attack or cardiacarrest and with a communication means, potentially contact emergencyservices directly without intervention of the wearer.

Other features and advantages of the invention will be found in thedetailed description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of a defibrillation electrode pad according to theinvention, positioned over the chest of a patient.

FIG. 2 is a view of the front display panel of a resuscitation controlbox according to the invention that houses electronic circuitry andprovides audible and visual prompting.

FIG. 3 is a cross-sectional drawing of the defibrillation electrode padof FIG. 1 taken along line 3-3.

FIG. 4 is a cross-sectional drawing of the defibrillation pad of FIG. 1taken along line 4-4.

FIG. 5 is a circuit diagram illustrating the circuit interconnectionsbetween the defibrillation electrode pad of FIG. 1 and the resuscitationcontrol box of FIG. 2.

FIGS. 6A and 6B are a flowchart illustrating the initial routine of aresuscitation system according to the invention.

FIGS. 7A, 7B, and 7C are a flowchart illustrating the “circulation help”routine of the resuscitation system.

FIG. 8 is a flowchart illustrating the “breathing help” routine of theresuscitation system.

FIGS. 9A and 9B are a flowchart illustrating the “airway help” routineof the resuscitation system.

FIG. 10 is a block diagram of the electronic circuitry of an alternativeimplementation.

FIG. 11 is a drawing of the defibrillation electrode assembly of anotheralternative.

FIGS. 12A-12C are diagrammatic views of three possible implementationsof first and second units.

FIGS. 13A and 13B are drawings of two alternative implementations of theelectrode pad assembly in which a handle is provided for the rescuer.

DETAILED DESCRIPTION

There are a great many possible implementations of the invention, toomany to describe herein. Some possible implementations that arepresently preferred are described below. It cannot be emphasized toostrongly, however, that these are descriptions of implementations of theinvention, and not descriptions of the invention, which is not limitedto the detailed implementations described in this section but isdescribed in broader terms in the claims.

With reference to FIG. 1, a defibrillation electrode pad 10, whichincludes high-voltage apex defibrillation electrode 12 and high-voltagesternum defibrillation electrode 14, is placed on the patient's chest 16and includes a region 18 on which a user may press to perform CPR.Legends on pad 10 indicate proper placement of the pad with respect tothe patient's collarbones and the chest centerline and the properplacement of the heel of the rescuer's hand.

A low-profile button panel 20 is provided on the electrode assembly.Button panel 20 has buttons 22, including buttons A (Airway Help), B(Breathing Help), C (Circulation Help) and PAUSE, and may also includeadjacent light emitting diodes (LEDs) 24 that indicate which button hasbeen most recently pressed. Button panel 20 is connected by a cable 23to a remote resuscitation control box 26, shown in FIG. 2. Button panel20 provides rigid support underneath buttons A, B, C, and PAUSE againstwhich the switches can be pushed in order to ensure good switch closurewhile the electrode rests on a patient. Button panel 20 includescomponents that make electrical contact with silver/silver-chlorideelectrical circuit components screen-printed on a polyester base ofdefibrillation electrode pad 10, as is described in detail below.

A pulse detection system based on shining light through the patient'svascular bed, e.g., a pulse oximetry system 52, is incorporated intodefibrillation electrode pad 10. Pulse oximetry system 52 includes a redlight-emitting diode, a near-infrared light-emitting diode, and aphotodetector diode (see FIG. 5) incorporated into defibrillationelectrode pad 10 in a manner so as to contact the surface of thepatient's chest 16. The red and near-infrared light-emitting diodes emitlight at two different wavelengths, which is diffusely scattered throughthe patient's tissue and detected by the photodetector diode. Theinformation obtained from the photodetector diode can be used todetermine whether the patient's blood is oxygenated, according to knownnoninvasive optical monitoring techniques.

In another implementation, the pulse detection system is aphonocardiogram system for listening to the sound of the victim's heart,rather than a pulse oximetry system. The phonocardiogram system includesa microphone and an amplifier incorporated within the electrode pad.Because a heart sound can be confused with microphone noise, the signalprocessing that must be performed by the microprocessor inside thecontrol box will be more difficult in connection with a phonocardiogramsystem than in connection with a pulse oximetry system. Nevertheless,there are programs available that can enable the microprocessor todetermine whether an ECG signal is present as opposed to microphonenoise.

Pulse oximetry is a well-developed, established technology, but itrequires good contact between the light sources and the victim's skin sothat light can shine down into the victim's vascular bed. Many victimshave lots of chest hair, which can interfere with good contact. It maybe desirable for different types of electrode pads to be available at agiven location (one having a pulse oximetry system and one having aphonocardiogram system) so that a rescuer can select an appropriateelectrode pad depending on the nature of the victim.

In another implementation, instead of providing a low-profile buttonpanel, a button housing can be provided that is affixed to an edge ofthe defibrillation electrode. The housing may be in the form of aclamshell formed of single molded plastic element having a hinge at anedge of the clamshell around which the plastic bends. The two halves ofthe clamshell can be snapped together around the electrode assembly.

The resuscitation control box (FIG. 2) includes an internal chargestorage capacitor and associated circuitry including a microprocessor,an further includes off/on dial 28, and a “READY” button 30 that therescuer presses immediately prior to application of a defibrillationshock in order to ensure that the rescuer is not in physical contactwith the patient. The microprocessor may be a RISC processor such as aHitachi SH-3, which can interface well with displays and keyboards, ormore generally a processor capable of handling DSP-type (digital signalprocessing) operations.

The resuscitation control box has printed instructions 32 on its frontface listing the basic steps A, B, and C for resuscitating a patient andgiving basic instructions for positioning the defibrillation electrodepad on the patient. A speaker 32 orally prompts the user to performvarious steps, as is described in detail below.

For example, the resuscitation control box instructs the user, byaudible instructions and also through a display 34 on the resuscitationcontrol box, to check the patient's airway and perform mouth-to-mouthresuscitation, and if the patient's airway is still blocked, to pressthe A (Airway Help) button on the button panel (FIG. 1), upon which theresuscitation control box gives detailed prompts for clearing thepatient's airway. If the patient's airway is clear and the patient has apulse but the patient does not breathe after initial mouth-to-mouthresuscitation, the resuscitation control box instructs the user pressthe B (Breathing Help) button, upon which the resuscitation control boxgives detailed mouth-to-mouth resuscitation prompts. If, during thedetailed mouth-to-mouth resuscitation procedure, the rescuer checks thepatient's pulse and discovers that the patient has no pulse, theresuscitation control box instructs the user to press the C (CirculationHelp) button.

During the circulation procedure, the resuscitation control box receiveselectrical signals from the defibrillation electrodes and determineswhether defibrillation or CPR should be performed. If the resuscitationcontrol box determines that defibrillation is desirable, theresuscitation control box instructs the user to press the “ready” buttonon the resuscitation control box and to stand clear of the patient.After a short pause, the resuscitation control box causes adefibrillation pulse to be applied between the electrodes. If at anypoint the resuscitation control box determines, based on the electricalsignals received from the electrodes, that CPR is desirable, it willinstruct the user to perform CPR.

Thus, the key controls for the system are on the electrodes attached tothe patient rather than the resuscitation control box. This is importantbecause it enables the rescuer to remain focused on the patient ratherthan the control box. The resuscitation control box gets its informationdirectly from the electrodes and the controls on the electrodes.

The resuscitation control box can sense electrical signals from thepatient's body during pauses between CPR compressions. Also, as isdescribed below, a compression-sensing element such as an accelerometeror a force-sensing element is provided in the region of thedefibrillation electrode pad on which the user presses to perform CPR.The purpose of the compression-sensing or force-sensing element is toallow the resuscitation control box to prompt the user to applyadditional compression or force, or to prompt the user to cease CPR ifthe user is performing CPR at an inappropriate point in time.

Referring to FIG. 4, in one implementation, each electrode 12, 14 (onlyelectrode 12 is shown) of defibrillation electrode pad 10 includes apolymer-based ink containing a silver/silver-chloride suspension, whichis screen-printed on a polyester or plastic base 36. The ink is used tocarry the defibrillation current. The screen-printing process firstinvolves applying a resist layer to the polyester base 36. The resistlayer is basically a loose mesh of nylon or the like, in which the holeshave been filled in at some locations in the mesh. Then, thesilver/silver-chloride ink is applied as a paste through the resistlayer in a squeegee-like manner. The ink squeezes through the screen andbecomes a solid layer. The ink may then be cured or dried. Thesilver/silver-chloride ink provides good conductivity and goodmonitoring capabilities.

Thus, the ink can be applied as pattern, as opposed to a solid sheetcovering the entire polyester base. For example, U.S. Pat. No. 5,330,526describes an electrode in which the conductive portion has a scallopedor daisy shape that increases the circumference of the conductiveportion and reduces burning of the patient. A conductive adhesive gel 38covers the exposed surface of each electrode.

In addition, electrical circuit components are also be screen printed onthe base, in the same manner as flat circuit components ofmembrane-covered, laminated panel controls.

Referring to FIG. 3, a rigid piece 40 of hard plastic, such as PVC orpolycarbonate, is laminated beneath substrate 36 and supports buttons A,B, C, and PAUSE. The rigid plastic piece 40 is glued onto substrate 36.Buttons A, B, C, and PAUSE consist of small metal dome snap-actionswitches that make contact between an upper conductive ink trace 42 andlower conductive ink traces 44, 46, 48, and 50. Buttons A, B, C, andPAUSE serve as controls that can be activated by the user that arephysically located either on or immediately adjacent to the electrodeassembly itself. Each of buttons A, B, C, and PAUSE may be associatedwith an adjacent light-emitting diode (LED). For example, LEDs may beglued, using conductive epoxy, onto silver/silver-chloride traces onsubstrate 36. An embossed polyester laminate layer 54 covers conductiveink trace 42 of buttons A, B, C, and PAUSE, and a foam layer 56 islaminated beneath rigid plastic piece 40.

Referring again to FIG. 4, defibrillation electrode pad 10 includes anextension piece that is placed directly over the location on thepatient's body where the rescuer performs chest compressions. Thisextension piece includes substrate 36, and a semi-rigid plasticsupporting member 58 laminated underneath substrate 36 that covers thechest compression area. Semi-rigid supporting member 58 providessomewhat less rigidity than rigid plastic piece 409 provided at thelocation of buttons A, B, C, and PAUSE (illustrated in FIG. 3).

In implementations having a force-sensing element, a polyester laminate60, and a force-sensing resistor having two layers of carbon-platedmaterial 62 and 64, are laminated between polyester substrate 36 andsemi-rigid supporting member 58. A suitable construction of theforce-sensing resistor is illustrated in the FSR Integration Guide &Evaluation Parts Catalog with Suggested Electrical Interfaces, fromInterlink Electronics. The electrical contact between the twocarbon-plated layers of material increases with increased pressure, andthe layers of force-sensing resistive material can provide a generallylinear relationship between resistance and force. Conductive ink traces66 and 68 provide electrical connections to the two layers of theforce-sensing resistor.

During chest compressions, the rescuer's hands are placed over theextension piece, and the force-sensing resistor of the extension pieceis used to sense the force and the timing of the chest compressions. Theforce-sensing resistor provides information to the resuscitation controlbox so that the resuscitation control box can provide the rescuer withfeedback if the rescuer is applying insufficient force. Theresuscitation control box also provides coaching as to the rate at whichCPR is performed. In certain situations, the resuscitation control boxindicates to the rescuer that CPR should be halted because it is beingperformed at an inappropriate time, such as immediately prior toapplication of a defibrillation shock when the rescuer's hands shouldnot be touching the patient, in which case the resuscitation control boxwill also indicate that the rescuer should stay clear of the patientbecause the patient is going to experience a defibrillation shock.

As is noted above, during CPR the rescuer pushes on the patient's chestthrough the extension piece in the vicinity of the electrodes. If theresuscitation control box were to perform analysis during the chestcompressions, the chest compressions would be likely to affect thesensed electrical rhythm. Instead, during the pauses between sets ofcompressions (for example, the pause after every fifth chestcompression), the resuscitation control box can perform anelectrocardiogram (ECG) analysis. The resuscitation control box mightdiscover, for example, that the patient who is undergoing CPR isexperiencing a non-shockable rhythm such as bradycardia, in which casethe CPR is required in order to keep the patient alive, but then theresuscitation control box may discover that the rhythm has changed toventricular fibrillation in the midst of CPR, in which case theresuscitation control box would instruct the rescuer to stop performingCPR so as to allow the resuscitation control box to perform moreanalysis and possibly apply one or more shocks to the patient. Thus, therescuer is integrated into a sophisticated scheme that allows complexcombinations of therapy.

In another implementation, a compression-sensing element such as anaccelerometer may be used in place of a force-sensing element. Theaccelerometer, such as a solid-state ADXL202 accelerometer, ispositioned at the location where the rescuer performs chestcompressions. In this implementation, the microprocessor obtainsacceleration readings from the accelerometer at fixed time intervalssuch as one-millisecond intervals, and the microprocessor integrates theacceleration readings to provide a measurement of chest compression. Theuse of an accelerometer is based on the discovery that it is moreimportant to measure how deeply the rescuer is compressing the chestthan to measure how hard the rescuer is pressing. In fact, everyvictim's chest will have a different compliance, and it is importantthat the chest be compressed about an inch and a half to two inches in anormal sized adult regardless of the victim's chest compliance.

FIG. 5 is a circuit diagram illustrating the circuit interconnectionsbetween the defibrillation electrode pad of FIG. 1 through the cable tothe resuscitation control box of FIG. 2. Sternum electrode 14 isconnected to HV+ at the resuscitation control box, and apex electrode 12is connected to HV−. A ground GND is connected to the upper conductiveink trace of buttons A, B, C, and PAUSE and to one of the layers of theforce-sensing resistor. The other layer of the force-sensing resistor isconnected to CPR FORCE, and the lower conductive ink traces associatedwith buttons A, B, C, and PAUSE are connected to BUTTON_DETECT throughresistors R1, R2, R3, and R4. As an alternative to the use of aforce-sensing resistor, a compression-sensing accelerometer 76 may beemployed, in which case CPR FORCE is replaced by CPR_ACCEL connected toaccelerometer 76. Red light-emitting diode 70, near-infraredlight-emitting diode 72, and photodetector diode 74 of the pulseoximetry system are connected to RLED, ILED, and ISENSE respectively, aswell as ground AGND. As an alternative to the use of a pulse oximetrysystem, a phonocardiogram system may be employed, in which case RLED,ILED, and ISENSE is replaced by SENSE connected to microphone 78 andamplifier 80.

FIGS. 6-9 illustrate the routine of the resuscitation system, which isbased on steps A, B, and C (airway, breathing, and circulation). Becausestep C includes defibrillation as well as chest compressions, all of theaspects of resuscitation are tied together in one protocol (actually, ifdefibrillation were considered to be a step D distinct from step C, thesequence of steps would be A, B, D, C).

The first thing the rescuer must do upon arriving at the patient is todetermine whether the patient is unconscious and breathing. The rescueropens the patient's airway, administers breaths to the patient if thepatient is not breathing, and checks to determine whether a pulse ispresent. If there is no pulse, rather than perform chest compressions asin standard CPR, the rescuer allows the resuscitation control box toanalyze the patient's electrical rhythm, and if the resuscitationcontrol box determines that the rhythm is shockable, the resuscitationcontrol box causes one or more shocks to be applied to the patient, andthen the rescuer performs chest compressions. Thus, there is provided afirst response system that can keep the patient viable until an advancedlife support time arrives to perform advanced techniques includingpacing, further defibrillation, and drug therapy.

If the resuscitation control box determines that it should apply one ormore defibrillation shocks to the patient, it is important that therescuer not be anywhere near the patient when the shocks are applied tothe patient. Prior to application of each shock, the resuscitationcontrol box instructs the rescuer to please press the “ready” buttonwhen everybody is clear of the patient. The pressing of the “ready”button verifies that the rescuer's hands are off of the patient.

When the resuscitation control box detects a shockable rhythm, theresuscitation control box provides shocks of appropriate duration andenergy (such as a sequence of shocks of increasing energy from 200Joules to 300 Joules to the highest setting, 360 Joules, with theresuscitation control box performing analysis after each shock todetermine whether another shock is required). If the defibrillationtherapy is successful, the patient's rhythm is typically converted fromventricular fibrillation, ventricular tachycardia, or ventricularflutter to bradycardia, idio-ventricular rhythm, or asystole, all ofwhich require CPR. It is rare to convert to a normal rhythm. Once theresuscitation control box has caused defibrillation shocks to be appliedto the patient, the resuscitation control box automatically senses thepatient's condition, and depending on the patient's condition willeither prompt the responder to perform CPR or will not prompt therespond to perform CPR.

Defibrillation equipment can be somewhat intimidating to rescuers whoare not medical professionals because the equipment can lead the rescuerto feel responsibility for having to save a loved one's life. It isimportant that the defibrillation equipment reduce this sense ofresponsibility. In particular, when the rescuer presses the “ready”button, rather than apply a shock immediately that will cause thepatient's body to jump dramatically, the resuscitation control box willthank the rescuer and instruct the rescuer to remain clear of thepatient and then wait for about two seconds (the resuscitation controlbox may describe this period to the rescuer as being an internal safetycheck, even if no substantial safety check is being performed). Thisprocess has an effect similar to a conversation that handsresponsibility to the resuscitation control box, which makes thedecision whether to apply the shock. Thus, the system maintains therescuer safety features of a semi-automatic external defibrillator,because the rescuer must press the “ready” button before each shock,while appearing to operate more as a fully automatic externaldefibrillator because the time delay immediately prior to each shockleaves the rescuer with the impression that operation of the equipmentis out of the hands of the rescuer. The use of CPR prompts incombination with the defibrillation also adds to the sense that therescuer is simply following instructions from the resuscitation controlbox.

With reference to FIGS. 6-9, when the rescuer turns the resuscitationcontrol box on (step 101), the resuscitation control box first informsthe rescuer that the rescuer can temporarily halt prompting by pressingthe PAUSE button (step 102), and then, after a pause, instructs therescuer to check responsiveness of patient, and if the patient isnon-responsive to call an emergency medical service (EMS) (steps 103,104). The resuscitation control box then instructs the rescuer to checkthe patient's airway to determine whether the patient is breathing(steps 105-107).

After a pause, the resuscitation control box then instructs the rescuerthat if the patient is breathing the patient should be placed on thepatient's side, unless trauma is suspected, and that the rescuer shouldpress the PAUSE button (steps 108-109). Then the resuscitation controlbox instructs the rescuer to perform mouth-to-mouth resuscitation if thepatient is not breathing (steps 110-114). Then the resuscitation controlbox instructs the rescuer to press an Airway Help button A if thepatient's airway is blocked, so that the resuscitation control box cangive prompts for clearing obstructed airways (steps 115 of FIG. 6B and147-158 of FIGS. 9A-9B).

Next, after a pause (step 116 a), if the resuscitation control box doesnot include pulse oximetry or phonocardiogram capability (step 116 b),the resuscitation control box instructs the rescuer to check thepatient's pulse (step 117). After another pause, the resuscitationcontrol box instructs the rescuer to press a Breathing Help button B ifthe patient's pulse is okay but the patient is not breathing, so thatthe resuscitation control box can give prompts for assisting thepatient's breathing (steps 118 and 119 of FIG. 7A and 140-146 of FIG.8). Light-emitting diodes adjacent the various buttons indicate whichbutton has been pressed most recently (only one light remains on at atime). The resuscitation control box next prompts the rescuer to contactan emergency medical system (step 120) and to open the patient's shirtor blouse and attach the adhesive pads (steps 122 f-122 h).

If the resuscitation control box does include pulse oximetry orphonocardiogram capability (step and 116 b), the resuscitation controlbox prompts the rescuer to open the patient's shirt or blouse and attachthe adhesive pads (steps 121 and 122 a). If the pulse oximetry orphonocardiogram system does not provide a valid pulsatile reading (step122 b), then the flow chart proceeds to step 117. If the pulse oximetryor phonocardiogram system does provide a valid pulsatile reading anddetects a pulse (steps 122 b and 122 c), then the resuscitation controlbox begins the breathing help routine (steps 122 d of FIG. 7B and step140 of FIG. 8). If the pulse oximetry or phonocardiogram system does notdetect a pulse, then the resuscitation control prompts the rescuer tocontact an emergency medical system (step 122 e), measures the impedanceof the patient to determine whether it is within an acceptable range forapplication of shocks (step 123) and determines whether the patient'srhythm is shockable (steps 124). If the rhythm is shockable, theresuscitation control box causes a sequence of shocks to be applied tothe patient, each shock requiring the rescuer first to press the “READY”button on the resuscitation control box (steps 124-131). After the lastshock in the sequence, or if the rhythm is non-shockable, theresuscitation control box prompts the rescuer in CPR (steps 132-139).The flowchart then returns to step 117.

FIG. 8 shows the steps 140-146 for prompting the rescuer to assist thepatient's breathing. After 12 breaths have been completed (step 144),the pulse oximetry or phonocardiogram system attempts to detect a pulse(step 145 a), or, if the system does not include a pulse oximetry orphonocardiogram system, the resuscitation control box prompts therescuer to check the patient's pulse. If no pulse is present, theresuscitation control box prompts the rescuer to press a CirculationHelp button C (step 145 b) that brings the rescuer back to thecirculation portion of the flowchart. Otherwise, if a pulse is detected,then the flow chart of FIG. 8 returns to step 142.

The combined defibrillation and CPR resuscitation assembly provided canbe less intimidating than conventional AEDs because the assembly is notdevoted solely to defibrillation. Moreover, the resuscitation assemblyis less intimidating because it accommodates common skill retentionproblems with respect to necessary techniques ancillary todefibrillation such as mouth-to-mouth resuscitation and CPR, includingthe appropriate rates of chest compression, the proper location forperforming compressions, the proper manner of tilting the patient'shead. In addition, because the rescuer knows that it may never even benecessary to apply a defibrillation shock during use of theresuscitation assembly, the rescuer may be more comfortable using theresuscitation assembly for mouth-to-mouth resuscitation and CPR. Unlikeprevious CPR prompting devices, the rescuer would be required to placethe electrode assembly on top of the patient, but the rescuer would dothis with the belief that the resuscitation assembly will be sensing thepatient's condition and that the likelihood that the resuscitationassembly is actually going to apply a shock is low. If, during thisresuscitation process, the resuscitation control box instructs therescuer to press the “READY” button so that a defibrillation shock canbe applied, the rescuer will likely feel comfortable allowing the shockto be applied to the patient. Basically, the resuscitation assemblysimply tells the rescuer what to do, and by that point, given that therescuer is already using the assembly, the rescuer is likely simply todo what the rescuer is told to do. Essentially, the rescuer will belikely to view the resuscitation assembly as simply being asophisticated CPR prompting device with an additional featureincorporated into it, and since rescuers are less likely to beintimidated by CPR prompting devices than AEDs, they will be likely touse the resuscitation assembly when it is needed.

FIGS. 10, 11, and 12A-12C show alternative implementations in which anelectrode pad assembly 10 is connected by a cable 212 to a first unit214 containing the electronics for CPR prompting and resuscitationcontrol. Another cable 216 connects the first unit to a second unit 218containing the electronics for defibrillation and pacing therapy. Athird cable 220 could be provided for making a direct connection fromthe second unit to the electrodes (FIG. 12B). The first unit 214 couldbe configured to receive the second unit 218 as an inserted module (FIG.12C), in which case the electrical connection between the units are madeinternally without the use of cable 216. The primary function of thefirst unit 214 is to provide processing and control for CPR functionssuch as CPR prompts. The primary function of the second unit 218 is toprovide processing and control of electrical therapy functions. Thefirst unit includes a CPR processor 170, a battery 178, ECG circuitry177 for amplifying and filtering the ECG signal obtained from thedefibrillation pads 12, 14, a microphone 78 for recording the rescuer'svoice as well as ambient sounds, an accelerometer 76, a real time clock187, and a speaker 182 for delivering prompts to the rescuer. The secondunit includes a therapy processor 171, a battery 179, buttons andcontrols 180, and memory 191.

The first unit could also be incorporated into the electrode padassembly rather than being a separate box. The electronics could beprovided on the rigid substrate 40 of the electrode pad assembly (FIG.1).

Separate batteries 178, 179 and controls 180, 181 may be provided forthe first (CPR) and second (therapy) units, thereby allowing theelectronics in the first unit to provide CPR prompting to the operatorwithout the need for the second unit. The cable 216 that connects thefirst and second units may be detachable. Memory 189 is provided in thefirst unit for storing information such as voice recording, ECG data,chest compression data, or electronic system status such as devicefailures that occur during daily self checks of the electronicsinitiated by a real time clock circuit.

The defibrillation electrode pad assembly 10 may incorporatedefibrillation electrodes composed of a material that can be heldagainst a patient's skin for extended periods of time (e.g., up to 30days).

As shown in FIGS. 13A and 13B, the pad assembly 10 may also incorporatefeatures on its upper surface facing the rescuer that provide a handle195 for the rescuer during performance of CPR. The handle could take theform of a fabric loop (FIG. 13B) or a more rigid polymer member (FIG.13A). The fabric could be sewn or adhered by adhesive or ultrasonicbonding to the pad 10 (FIG. 13B). The polymer handle could also bebonded by adhesive or ultrasonic bonding to the pad (FIG. 13A). It hasbeen shown in studies that the maintenance of pressure on the chestduring the decompression phase of chest compression results in asignificant decrease in the effectiveness of the chest compressions. Thehandle 195 motivates the rescuer to pull up at least slightly during thedecompression phase. The adhesive gel of the electrode pad, or otheradhesive, can extend under the region where the rescuer's hands areplaced during compression thus providing adhesion of the pad to the skinwhile the rescuer pulls on the handle during the decompression phase.Pulling up on the chest during the decompression phase has been shown toheighten negative intrathoracic pressure, increasing venous return andthus increasing blood flow during chest compressions.

In another implementation, the first unit may be adapted to be supportedby the patient for long periods of time. The unit could be incorporatedinto the electrode pad assembly as suggested above, or it could be aseparate unit configured to be worn by the patient. In such animplementation, the electronics of the first unit are designed to allowfor long term monitoring of the patient's condition via the ECG 177 andphysiological monitoring 176 circuitry. If a physiological condition isdetected that is deemed hazardous to the patient by the CPR processor170, based on analysis of the ECG and other physiological parameters, analarm is sounded to the patient via the speaker 182.

An activity sensor and associated circuitry can inform the CPR processorof whether the patient is moving. For example, accelerometer 76 couldserve as the activity sensor, and detect whether or not the patient ismoving. Patient motion may be detected using a variety of differentalgorithms, including, for example the following: The accelerationsignal is integrated over one-second intervals to provide an estimate ofvelocity. Velocity is integrated over the same one-second intervals toprovide an estimate of displacement. The root means square velocity iscalculated for each one-second interval. If either the RMS velocityexceeds 0.2 cm/s or the peak displacement exceeds 0.5 cm, the patient isdetermined to be moving.

If the algorithm determines that a cardiac emergency event is occurring,the first unit can send a message directly to a medical emergencyresponse system, such as 911. This can be done using a variety of knowncommunication techniques, e.g., Bluetooth, cellular phone, UltraWideband (UWB). If the activity sensor has determined that the patientis still moving during the cardiac emergency, the unit could also issuea prompt indicating, “Call 911 Immediately!”

The first unit will be able to determine the orientation of the patient,e.g., based on the accelerometer output. It can detect if a patient hasfallen down and initiate a message to the emergency system. It can alsodetermine whether the patient is lying on his back, the properorientation for doing CPR. Thus, a specific prompt can be provided tothe rescuer that tells them to roll the patient on their back prior tobeginning CPR, should the device detect an improper orientation of thepatient.

Other implementations may include signal analysis software forpredicting the risk of a heart attack. When a threshold is exceeded inthe value of that risk probability, a voice prompt may be provided tothe patient via the speaker 182 to contact the medical emergency system.By using the motion detection capabilities of the accelerometer tomeasure and track a patient's activity level (PAL), and combining theactivity level calculation with measurements of the ECG 177, e.g.,ST-segment elevation (STE), the first unit is able to provide apredictor of the risk of an impending heart attack or cardiac arrest. AnST segment elevation exceeding a threshold such as 300 microvolts on theECG provides an indicator of impending heart attack. In the preferredembodiment, ST segment elevation in the presence of increased physicalactivity is an indication of further risk of potential cardiac arrest.The calculation of risk probability may be accomplished by firstperforming a logistic regression of variables such as STE and PAL aspredictors of cardiac arrest within 24 hours. The calculation may takethe form of a linear regression equation such as

0.24STE+0.12PAL=RISK.

Alternatively, nonlinear regression may be performed to allow for amultiplicative term such as

0.24STE+0.12PAL+0.54(STE*PAL)=RISK.

The multiplicative term heightens the importance of STE in the presenceof PAL.

Parameters such as STE, PAL and RISK may additionally be stored inmemory and multiple readings and calculations performed over time. Thesequence of readings may then be analyzed for trends in thephysiological state of the patient that can augment the RISK calculationtaken at a single point in time. For instance, if STE is found to besteadily rising over a series of readings, the voice prompt may betriggered sooner than at a fixed threshold of 300 microvolts.

Additionally, the ECG may be analyzed to determine the interval betweenadjacent R-waves of the QRS complexes and using this interval tocalculate heart rate variability as a running difference betweenadjacent R-R intervals. It is known that the R-R interval will varyfollowing an ectopic beat or ventricular premature contraction (VPC). Ina healthy heart, the R-R interval will decrease immediately followingthe VPC followed by a gradual return to steady state; a heart with anincreased risk of heart attack will show a decreased level ofvariability. This effect is sometimes called heart rate turbulence. Twovariables are calculated: (1) the Relative Change in R-R interval (RCRR)between pre- and post-VPB R-R intervals,

RCRR=(R-R pre-VPB−R-R post-VPB)/R-R pre-VPB

and (2) the slope of the change of R-R interval (SRR) while it isundergoing its post-VPB decrease. If the RCRR is non-negative and theslope SRR does not steeper than −2 ms/R-R interval then the patient isconsidered as at risk. Alternatively, the individual calculations may beincluded along with STE and PAL to create an integrated measurementvector as discussed in the preceding paragraphs. Other signal analysisalgorithms may incorporate analysis of heart rate variability in thefrequency domain, wavelet domain or using non-linear dynamics-basedmethods.

Since VPBs are often rare events, the defibrillation electrode pad 10may include circuitry to stimulate the patient with a single pulse oflow enough amplitude to cause a VPB without undue discomfort to thepatient, under the patient's control. An additional control is providedon the low-profile button panel 20 so that the patient may initiate thepulse under their control. Alternatively, the device is programmed toautomatically deliver the pulse at regular intervals such as at 24-hourintervals, at a time of day when the patient may conveniently haveaccess to the device, such as in the morning. While the pulse generator186 may be located in the second (therapy) unit, it is preferablycontained as part of the first (CPR) unit.

In another implementation, the activity monitoring capability of thefirst unit may be utilized so that the activity state of the patient iscontinuously monitored. Using the activity monitoring capability and areal time clock 187, the first unit may detect when a patient has wokenup in the morning. After there has been 10 minutes of regular motiondetected, the unit may prompt the patient that it would like to performa test. If the patient assents to the test indicated by a press of theTEST button on the low-profile button panel 20, the unit will send out asmall current pulse, preferably a 40 millisecond pulse of 75 mAamplitude that is synchronized to the patient's ECG so that it occursapproximately 200 mS prior to the R-wave and after the T-wave so as notto introduce any arrhythmias. The pulse will safely cause a VPB in thepatient which can then be used to measure the autonomic response to aVPB to provide regular calculations of the autonomic response to a VPBas measured by such parameters, though not limited to, STE and PAL, andproviding a daily update to the RISK calculation.

Additional physiological measurement, preferably that of blood pressure,may be incorporated into the RISK calculation. A sudden change insystolic or mean arterial blood pressure of greater than 10-15 points isindicative of an increased risk of cardiac arrest. In the preferredembodiment, the blood pressure measurement device would be a handheld,inflated cuff blood pressure device 188. The blood pressure cuff 188would have wireless communication capability with the CPR Processor 170and at the conclusion of each measurement, the blood pressure readingalong with a date and time stamp would be stored in memory 189 of theCPR Processor 170 for subsequent use in calculating RISK. This schemewould allow the patient to carry the small blood pressure cuff alongwith them during their daily activities and take blood pressuremeasurements at regular intervals without having to return home.Alternatively, the blood pressure measurement device may communicatewith the therapy processor and may additionally get power from and bephysically connected to the second (therapy) unit by a cable. Thepatient will then be required to take regular blood pressure readings atthe second unit, typically a larger device that may or may not beportable. Communication of the blood pressure readings may beaccomplished over a cable between the first (CPR) and second units(therapy) units, e.g., cable 216, or wirelessly, using such technologyas Bluetooth.

The second unit 218 may in some implementations be thought of as anenergy delivery unit (EDU), in which case it would incorporate adefibrillator 172, pacer 173, or other electrical therapy 174. In someimplementations, the EDU would be small and light enough to be worn in aharness or belt to be carried around continuously by the patient. TheEDU 218 may in some cases not contain a therapy processor 171, but be a“dumb” device that requires the controls provided by connection to theprocessor in the first (CPR) unit, e.g., on the defibrillator pad 10, inorder to deliver electrical therapy to the patient.

In some cases, the patient may not even own an EDU due to thesignificant costs inherent in the high-voltage components necessary. Thepatient would only own the first unit and defibrillator pad, as thecomponents incorporated in them are less expensive, e.g., they can bemanufactured from less-expensive, consumer-type electronics. In such acase, when the patient did not own the EDU, and had a heart attack, abystander or family member who encountered the cardiac arrest victimwould be prompted to begin CPR. It has been shown now in several studiesthat performing good CPR for extended periods prior to delivery of ashock are not only not detrimental to long term survival, but in factincrease survival rates. CPR would thus begin with built-in promptingand when the paramedic arrives with the defibrillator it can beconnected to the pads to deliver the electrical therapy. If the first(CPR) unit is separate from the electrode pad assembly, the EDUconnection to the electrodes could be direct, or via a cable connectedto the first (CPR) unit. If the defibrillator is an EDU or othercompatible device, patient and performance data stored by the first(CPR) unit may be downloaded to the defibrillator.

Many other implementations of the invention other than those describedabove are within the invention, which is defined by the followingclaims. For example, the defibrillation pads 10, 12 may be separablefrom the CPR-prompting first unit and be connected at the time that theEDU is brought to the scene; the defibrillation pads may be connectedboth electrically and mechanically to the CPR-prompting first unit atthat time. A greater amount of the control functionality may be put intothe first unit, leaving essentially only the circuitry for providing thedefibrillation pulses in the second unit. The first unit may beincorporated into the defibrillation electrode pad assembly, or made aseparate unit connected to the pad assembly by one or more cables. Thesecond unit may connect to the first unit by one or more cables, or by awireless connection. The defibrillation pulses may pass through thefirst unit (FIG. 12A), or be routed directly to the defibrillationelectrodes via one or more cables running from the second unit to theelectrodes (FIG. 12B). The second unit may connect to the first unit bybeing plugged into the first unit (FIG. 12C), without the need for acable (e.g., the second unit could be a defibrillation module that plugsinto the first unit).

In some implementations the second (therapy) unit can provide pacingtherapy as well as defibrillation therapy. Pulse detection methods otherthan pulse oximetry and phonocardiogram may be employed. Any methodcapable of detecting a victim's pulse can be used for pulse detection.

What is claimed is:
 1. A cardiac monitoring system for monitoring a cardiac condition of a patient, comprising: a long term ECG monitoring unit configured to be supported by the patient for long periods of time comprising: a power source; one or more electrodes electrically attached to the long term ECG monitoring unit and configured to be worn by the patient for extended periods of time; circuitry for receiving an ECG signal of the patient via the electrodes; at least one processor operatively coupled to the circuitry for monitoring the ECG signal of the patient, the at least one processor configured to: analyze the ECG signal of the patient, wherein the analyzing comprises determining one or more intervals between adjacent R waves of QRS complexes in the ECG of the patient; and calculating a heart rate variability based on the determined one or more intervals between adjacent R waves of the QRS complexes in the ECG of the patient; and output the heart rate variability for determining a risk of a cardiac event in the patient based at least in part on the heart rate variability.
 2. The cardiac monitoring system of claim 1, further comprising a defibrillator unit configured to be electrically connected by a cable to the long term ECG monitoring unit.
 3. The cardiac monitoring system of claim 2, further comprising at least two defibrillator electrodes electrically coupled to the defibrillator unit.
 4. The cardiac monitoring system of claim 3, further comprising a conductive adhesive disposed on one or more surfaces of the at least two defibrillation electrodes.
 5. The cardiac monitoring system of claim 1, wherein the one or more electrodes are connected by at least one cable to the long term ECG monitoring unit.
 6. The cardiac monitoring system of claim 1, wherein the long term ECG monitoring unit comprises a first unit that is operatively coupled to a second unit.
 7. The cardiac monitoring system of claim 6, wherein the long term ECG monitoring unit is in wireless communication with the second unit.
 8. The cardiac monitoring system of claim 1, wherein monitoring the cardiac condition of the patient comprises analyzing the ECG signal for one or more cardiac parameters for determining the risk of the cardiac event.
 9. The cardiac monitoring system of claim 1, wherein the cardiac event comprises sudden cardiac arrest.
 10. The cardiac monitoring system of claim 1, wherein the long term ECG monitoring unit is configured communicate with a remote medical response system.
 11. The cardiac monitoring system of claim 1, wherein the long term ECG monitoring unit is configured communicate with a remote medical response system via at least one of Bluetooth connection and a cellular network connection.
 12. The cardiac monitoring system of claim 1, wherein the heart rate variability is based on a running difference between adjacent R-R intervals.
 13. The cardiac monitoring system of claim 1, wherein the heart rate variability can be analyzed in at least one of a frequency domain and wavelet domain.
 14. The cardiac monitoring system of claim 1, further comprising an input device configured to receive an input from the patient.
 15. The cardiac monitoring system of claim 1, further comprising an input device configured to allow the patient to indicate a symptom to the long term ECG monitoring unit.
 16. The cardiac monitoring system of claim 1, further comprising a memory and wherein the at least one processor is configured to record ECG information of the patient and store the ECG information to the memory.
 17. The cardiac monitoring system of claim 1, further comprising a speaker for issuing prompts to the patient.
 18. The cardiac monitoring system of claim 1, further comprising a display panel for providing visual prompts to the patient.
 19. The cardiac monitoring system of claim 1, wherein monitoring the cardiac condition of the patient comprises monitoring for at least one of a bradycardia, tachycardia, or a ventricular flutter in the ECG signal of the patient.
 20. A cardiac monitoring system for monitoring a cardiac condition of a patient, comprising: a first unit comprising a long term ECG monitoring unit configured to be supported by the patient for long periods of time comprising: a power source; one or more electrodes electrically attached to the long term ECG monitoring unit and configured to be worn by the patient for extended periods of time; circuitry for receiving an ECG signal of the patient via the electrodes; and at least one processor electrically coupled to the circuitry for monitoring the ECG signal of the patient, the at least one processor configured to: analyze the ECG signal of the patient, wherein the analyzing comprises determining one or more intervals between adjacent R waves of QRS complexes in the ECG of the patient; and calculating a heart rate variability based on the determined one or more intervals between adjacent R waves of the QRS complexes in the ECG of the patient; and output the heart rate variability for determining a risk of a cardiac event in the patient based at least in part on the heart rate variability; and a second unit communicably coupled to the first unit, wherein the second unit is configured to be small, light, and carried around continuously by the patient.
 21. The cardiac monitoring system of claim 20, wherein the second unit comprising a defibrillator unit configured to be electrically connected by a cable to the long term ECG monitoring unit.
 22. The cardiac monitoring system of claim 21, further comprising at least two defibrillator electrodes electrically coupled to the defibrillator unit.
 23. The cardiac monitoring system of claim 20, wherein monitoring the cardiac condition of the patient comprises analyzing the ECG signal for one or more cardiac parameters for determining the risk of the cardiac event.
 24. The cardiac monitoring system of claim 20, wherein the long term ECG monitoring unit is configured communicate with a remote medical response system.
 25. The cardiac monitoring system of claim 20, wherein monitoring the cardiac condition of the patient comprises monitoring for at least one of a bradycardia, tachycardia, or a ventricular flutter in the ECG signal of the patient.
 26. A cardiac monitoring method for monitoring a cardiac condition of a patient by a long term ECG monitoring unit, comprising: receiving an ECG signal of the patient via one or more electrodes electrically attached to the long term ECG monitoring unit, wherein the one or more electrodes and the long term ECG monitoring unit are configured to be worn by the patient for extended periods of time; determining one or more intervals between adjacent R waves of QRS complexes in the ECG of the patient; calculating a heart rate variability based on the determined one or more intervals between adjacent R waves of the QRS complexes in the ECG of the patient; and outputting the heart rate variability for determining a risk of a cardiac event in the patient based at least in part on the heart rate variability.
 27. The cardiac monitoring method of claim 26, further comprising analyzing the ECG signal of the patient to detect the cardiac event; and providing a therapeutic shock to the patient based on the analysis if the cardiac event comprises a shockable electrical rhythm in the patient.
 28. The cardiac monitoring method of claim 26, wherein monitoring the cardiac condition of the patient comprises analyzing the ECG signal for one or more cardiac parameters for determining the risk of the cardiac event.
 29. The cardiac monitoring method of claim 26, further comprising analyzing the ECG signal of the patient to determine a cardiac event; and causing the long term ECG monitoring unit to communicate with a remote medical response system on detecting the cardiac event.
 30. The cardiac monitoring method of claim 26, wherein monitoring the cardiac condition of the patient comprises monitoring for at least one of a bradycardia, tachycardia, or a ventricular flutter in the ECG signal of the patient. 